Badly missing some info here! You get the 12v red light ok if the "110v breaker is on."
But not if on battery and no shore power or gen? If so, that means your battery 12v is not reaching the DC fuse panel to run things, so no lights , no fans?
If you do have lights and fans but no water heater that is another story.
It appears you have a working converter to supply 12v when you have 120v, but not clear whether you have battery to the 12v whether any 120v or not.
That can mean the battery disconnect (if fitted) is open, or else the battery fuse (or DC circuit breaker) is blown down by the battery close to the pos post, or a dead battery.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.